The present invention relates, in general, to pneumatic braking systems such as are typically employed on rail transport vehicles (e.g., trains) and other relatively large wheeled transport vehicles (e.g., heavy trucks). More particularly, the present invention relates to a so-called xe2x80x9celectronically controlled pneumaticxe2x80x9d (hereinafter xe2x80x9cECPxe2x80x9d) type of braking system for such vehicles, most particularly ECP braking systems for trains and other rail transport vehicles.
The principles of a pneumatic braking system are well understood by those of ordinary skill in the relevant art. Typically, an onboard air compressor furnishes and replenishes as necessary compressed air to the system. A so-called xe2x80x9cmain reservoirxe2x80x9d is typically employed to maintain a substantially constant feed pressure to the system downstream thereof. The main reservoir is recharged by the onboard compressor whenever its pressure drops below a predetermined level.
A train xe2x80x9cconsistxe2x80x9d is formed of a number of related railcars linked end to end. The main reservoir, normally located in a forward locomotive along with the compressor, feeds a pneumatic line, commonly referred to as a xe2x80x9cbrake pipexe2x80x9d which typically extends the length of the train. In the formation of a train consist, the individual brake pipe sections located on each individual railcar are linked together through pneumatic couplings. On each individual railcar, a xe2x80x9cbranch pipexe2x80x9d supplies compressed air from the brake pipe running the length of the train to the individual braking components of the individual railcar, which typically include a so-called xe2x80x9cAB-Type control valvexe2x80x9d (also sometimes referred to as a xe2x80x9ctriple valvexe2x80x9d), an xe2x80x9cauxiliary reservoirxe2x80x9d, an xe2x80x9cemergency reservoirxe2x80x9d and the brake cylinders of the railcar. [Examples of AB-Type control valves are the ABD, ABDX and ABDW control valves currently or previously manufactured by Westinghouse Air Brake Company, i.e., xe2x80x9cWABCOxe2x80x9d.] During times when the brakes are xe2x80x9creleasedxe2x80x9d (e.g., no braking force being applied), compressed air from the pneumatic brake pipe is supplied via the branch line to maintain a predetermined compressed air charge within the auxiliary and emergency reservoirs of each railcar in the train consist. In some designs, a so-called xe2x80x9ccombined auxiliary and emergency reservoirxe2x80x9d is provided on a railcar. The brakes on an individual railcar are applied by supplying compressed air from at least the auxiliary/emergency reservoir(s) located on the railcar to the brake cylinders of the railcar. The compressed air displaces the pistons of the brake cylinders to apply a mechanical braking force to the wheels of the railcar.
In the conventional pneumatic braking system, as originally developed, the only means for actuating the transfer of compressed air from the auxiliary/emergency reservoir(s) to the brake cylinders is through the brake pipe itself. An engineer or other operator lowers the brake pipe pressure, e.g., by manipulating a brake lever on a brake control panel located in the locomotive. For example, the brake pipe pressure can be lowered by venting the brake pipe to atmosphere in response to movement of a control handle by the engineer.
The AB-Type control valves located on each individual railcar are constructed such that they respond to a lowered brake pipe pressure by supplying compressed air from at least the auxiliary reservoir located on each railcar to the brake cylinders of the railcar, thereby applying the brakes of the railcar. The amount of air pressure supplied from the auxiliary reservoir to the brake cylinders by the AB-Type control valves is proportional to the amount by which the brake pipe pressure is lowered by the engineer. Typically, the control handle allows the engineer to apply a continuously variable braking force beginning with a so-called xe2x80x9creleasexe2x80x9d position (in which the brake pipe pressure is at a maximum and the braking pressure applied at the individual railcars is therefore at a minimum, e.g., the brakes are released), through a xe2x80x9cminimum servicexe2x80x9d brake application, a xe2x80x9cfull servicexe2x80x9d brake application and ultimately to an xe2x80x9cemergencyxe2x80x9d brake application (in which the brake pipe pressure is at a minimum and the braking pressure applied at the individual railcars is therefore at a maximum). Other braking applications may be available to the engineer such as suppression and continuous service, but the principle is basically the same, namely, that the engineer""s movement of the braking control handle lowers the brake pipe pressure, and the AB-Type control valves located in the individual railcars respond by supplying air from the auxiliary/emergency reservoir(s) located on the individual railcars to the brake cylinders proportionately according to the degree by which the brake pipe pressure is lowered by the engineer.
When the engineer moves the control handle to the xe2x80x9cemergencyxe2x80x9d position, the brake pipe pressure is precipitously reduced. As is well understood in the art, the individual AB-Type control valves on the individual railcars are constructed such that, when the brake pipe pressure drops below a determined pressure, the AB-Type control valves transfer compressed air from both the auxiliary and emergency reservoirs on each railcar to the brake cylinders of the railcar, resulting in a greater mechanical braking force being applied than in a service braking application, wherein only compressed air from the auxiliary reservoirs is supplied to the brake cylinders.
One advantage of the above-described conventional pneumatic braking system is that it provides a xe2x80x9cfail safexe2x80x9d mechanism. Since the brakes at the individual railcars are applied in response to a decrease in brake pipe pressure, a rupture of the brake pipe, a failure of the compressor, etc. results in the brakes being applied and not in a brake failure. In view of the dire consequences of brake failure on a railway train, it is understandable that pneumatic braking development has been characterized by the fail safe concept.
However, a limitation of such a conventional pneumatic braking system described above that has been long appreciated is the delay in braking that occurs as the change in brake pipe pressure propagates along the length of a train. For example, it has been estimated that a brake pipe pressure drop in a freight train of approximately one mile in length may take about one minute to travel the length of the train if it is a service brake application and about one-half minute if it is an emergency brake application.
To overcome this limitation, so-called xe2x80x9celectronically controlled pneumaticxe2x80x9d (or xe2x80x9cECPxe2x80x9d) braking systems have been developed. ECP braking systems also utilize the concept of control valves located on each railcar which transfer previously stored compressed air from auxiliary/emergency reservoir(s) located on the railcars to the brake cylinders thereof to generate a braking force. However, in an ECP braking system, the control valves can be electrically actuated (i.e., through electropneumatic valves). Therefore, signals to the railcar control valves are transmitted at least electrically, rather than only through the brake pipe pressure, thereby substantially eliminating the propagation delay along a long freight train mentioned above.
In a typical implementation of an ECP braking system on a freight train, the lead locomotive is provided with a master controller (e.g., microprocessor controlled) which receives input data signals describing the degree of braking application applied by the engineer via the brake control handle. The master controller then formulates braking commands for the railcars and sends electrical braking command signals to individual car control units or xe2x80x9cCCUxe2x80x9ds (e.g., also microprocessor controlled) located on each individual railcar which describe the degree of braking to be applied by each individual railcar. The electrical braking command signals sent by the master controller typically describe the braking application in terms of a percentage of the pressure required for a full service brake application, for example, with 0% indicating a release of brakes, 15% indicating a minimum service brake application, 100% indicating a full service brake application and 120% indicating an emergency brake application.
The communication signals between the master controller and the individual CCU""s are typically conveyed by an electrical communication line (e.g., an xe2x80x9celectrical trainlinexe2x80x9d) which runs from railcar to railcar throughout the length of the train. Like the pneumatic brake pipe, the electrical trainline consists of a sequential series of individual segments which are joined end to end during the formation of a train consist.
In order to provide for a redundant or fail safe manner of operation, the pneumatic braking system is frequently retained on trains having an ECP braking system implementation. For example, the ECP electrical trainline may be employed to communicate both service and emergency braking applications to the individual railcars, while the pneumatic brake pipe may be employed to communicate only backup emergency braking applications to the individual railcars.
As noted above, during an emergency braking operation, the brake pipe pressure is dropped as rapidly as possible, since it is the severely reduced brake pipe pressure which initiates the transfer of compressed air from both the auxiliary and emergency reservoirs to the brake cylinders. However, on long trains, particularly long freight trains, brake pipe pressure changes, even an emergency brake pipe pressure reduction, can take up to one-half minute to propagate the length of the train.
The present invention is directed to producing a very rapid drop in the brake pipe pressure upon the detection of conditions indicating that an emergency brake application has been initiated. The present invention is particularly adapted to use in conjunction with an ECP type of braking system. However, the present invention could also be used in conjunction with the conventional type of pneumatic braking system described above.
One object of the present invention is the provision of an electronic vent valve for attachment to the brake pipe of an electronically controlled pneumatic braking system for quickly and precipitously lowering the brake pipe pressure in response to a received electrical signal indicating the initiation of an emergency braking condition, thereby ensuring that the control valve of the pneumatic braking system will respond to the rapidly lowered brake pipe pressure by supplying an appropriate compressed air charge from the onboard auxiliary/emergency reservoirs to the brake cylinders so as to initiate the desired emergency braking action.
Another object of the present invention is the provision of such an electronic vent valve which is additionally capable of monitoring the existing brake pipe pressure and opening the vent valve in response to a negative rate of change in the brake pipe pressure (dP/dt) that exceeds a threshold rate of pressure change determined to be indicative, in and of itself, of an emergency braking condition.
A further object of the present invention is the provision of such an electronic vent valve which can, upon determining the existence of an emergency braking condition, perform optional emergency subroutines, such as, for example, determining subsequent rates of change of brake pipe pressure (dP/dt) and reporting such rates of change of brake pipe pressure to a master controller unit, actuating appropriate warning indicators, attempting to reactuate the vent, etc.
A still further object of the present invention is the provision of such an electronic vent valve which is capable of performing periodic test subroutines to determine whether it is in proper operational condition.
A yet further object of the present invention is the provision of such an electronic vent valve that is reliable in operation and efficient in manufacture.
In addition to the objects and advantages of the present invention described above, various other objects and advantages of the invention will become more readily apparent to those persons skilled in the relevant art from the following more detailed description of the invention, particularly when such description is taken in conjunction with the attached drawing Figures and with the appended claims.
In one aspect, the invention generally features an electronically controlled vent valve for a pneumatic brake system, the pneumatic brake system including a brake pipe carrying compressed air, the electronically controlled vent valve including a valve for connecting to the brake pipe and for being in fluid communication with the compressed air carried by the brake pipe, the valve having an open position for substantially venting the compressed air from the brake pipe and a closed position for substantially retaining the compressed air within the brake pipe, an electrically operated actuator for moving the valve between the open position and the closed position and a control circuit for controlling the electrically operated actuator to move the valve between the open position and the closed position.
In another aspect, the invention generally features an electronically controlled vent valve for an electronically controlled pneumatic braking system, the electronically controlled pneumatic braking system having a plurality of braking sites at which a braking force can be applied, the electronically controlled pneumatic braking system including a master controller processing circuit for generating and supplying electrical braking command signals and an individual braking control unit located proximate each of the plurality of braking sites for receiving the electrical braking command signals generated and transmitted by the master controller processing circuit, the electronically controlled pneumatic braking system further including a brake pipe supplying compressed air to the plurality of braking sites, the electronically controlled vent valve including a valve housing for connecting to the brake pipe and for receiving the compressed air from the brake pipe, a valve member disposed within the valve housing, the valve member having an open position for substantially venting the compressed air from the valve housing and a closed position for substantially retaining the compressed air within the valve housing, an electrically operated actuation mechanism for moving the valve member between the open and closed positions and an electronic control circuit for controlling the electrically operated actuation mechanism to thereby cause the valve member to move between the open and closed positions.
The present invention will now be described by way of a particularly preferred embodiment, reference being made to the various Figures of the accompanying drawings.